Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/417—Polyolefins
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
  • H01M50/406—Moulding; Embossing; Cutting
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/443—Particulate material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
  • H01M50/491—Porosity
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to the technical field of lithium-ion batteries, specifically to a microporous separator for lithium battery and a preparation method thereof.
• Polyolefin-based microporous membrane is widely used as a separation membrane for separation and selective permeation of various substances, and an isolation material, etc.
• polyolefin-based microporous membrane is used as a precision filtration membrane, a separator for fuel cell, a separator for capacitor, a base material for functional membrane which is filled with functional materials in pores in order to show new functions, a separator for battery, etc.
• polyolefin-based microporous membrane is particularly suitable for use as a separator for lithium-ion batteries widely used in laptops, mobile phones, digital cameras, and the like. As its reasons, it can be enumerated that the polyolefin-based microporous membrane has excellent membrane mechanical strength and shutdown characteristics.
• microporous separator for lithium battery good resilience performance in a thickness direction is also required to ensure that the microporous separator undergoes smaller deformation in the thickness direction when the battery is subjected to impact in the thickness direction, and can be recovered more quickly when the impact force is removed, thereby ensuring the safety performance of the battery.
• the present invention achieves a separator for lithium-ion battery with high resilience rate in a thickness direction by controlling a quantity proportion of high molecular weight chain segments in the polyolefin resin.
• the separator of the present invention also has a small compression deformation rate and a large resilience amount.
• a first aspect of the present invention provides a microporous separator for lithium battery, including a polyolefin resin.
• the microporous separator has a melt index of 0.04 g/10min - 3 g/10min, preferably 0.08 g/10min - 0.4 g/10min.
• a quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight of 2 million to 5 million is 5 mol% - 8 mol%, preferably 5 mol% - 7 mol%; and a resilience speed of the microporous separator in its thickness direction is greater than or equal to 2 ⁇ 10 -4 ⁇ m/s, preferably, greater than or equal to 3 ⁇ 10 -4 ⁇ m/s, greater than or equal to 5 ⁇ 10 -4 ⁇ m/s, greater than or equal to 7 ⁇ 10 -4 ⁇ m/s, greater than or equal to 8 ⁇ 10 -4 ⁇ m/s, and most preferably greater than or equal to 10 ⁇ 10 -4 ⁇ m/s; and
• the quantity proportion of polyolefin segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million in the microporous separator is 0 mol% - 1 mol%, preferably 0.5 mol% - 1 mol%.
• the microporous separator satisfies one or more of the following:
• the polyolefin resin has a molecular weight distribution between 3 and 5, preferably between 3.5 and 4.5
• the quantity proportion of polyolefin chain segment ingredients with the weight-average molecular weight of 2 million to 5 million in the polyolefin resin is 5 mol% - 9 mol%, preferably 5 mol% - 8 mol%, and more preferably 6 mol% - 8 mol%.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million in the polyolefin resin is 0 mol% - 2 mol%, preferably 1 mol% - 1.5 mol%.
• the microporous separator is a separator prepared by a wet process.
• the polyolefin resin is selected from polyethylene (including, for example, LDPE, LLDPE, HDPE, UHDPE), polypropylene, polybutene, polymethylpentene, a copolymer thereof, or a mixture thereof.
• the microporous separator has an average pore diameter of 25 nm -50 nm, preferably 30 nm - 45 nm; and the microporous separator has a thickness of 1 ⁇ m - 30 ⁇ m, preferably 4 ⁇ m - 12 ⁇ m.
• a second aspect of the present invention provides a preparation method for a microporous separator for lithium battery, including the following steps:
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million in the polyolefin resin is 0 mol% - 2 mol%, preferably 1 mol% - 1.5 mol%.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million in the microporous separator is 0 mol% - 1 mol%, preferably 0.5 mol% -1 mol%.
• the polyolefin resin has a molecular weight distribution between 3 and 5, preferably 3.5-4.5.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight of 2 million to 5 million in the microporous separator is 5 mol% - 8 mol%, preferably 5 mol% - 7 mol%.
• a resilience speed of the microporous separator in its thickness direction is greater than or equal to 2 ⁇ 10 -4 ⁇ m/s, preferably greater than or equal to 3 ⁇ 10 -4 ⁇ m/s, greater than or equal to 5 ⁇ 10 -4 ⁇ m/s, greater than or equal to 7 ⁇ 10 -4 ⁇ m/s, greater than or equal to 8 ⁇ 10 -4 ⁇ m/s, and most preferably greater than or equal to 10 ⁇ 10 -4 ⁇ m/s; and
• a weight ratio of the polyolefin resin to the plasticizer is between 15:85 and 35:65, preferably between 18:82 and 23:77.
• an extruder is used for melting and blending, and the extruder has parameters including: an extruder temperature of 150 °C - 260 °C and an extruder screw speed of 60 r/min - 125 r/min.
• the casting roller has a roll speed of 3 m/min - 8 m/min, and the die has a temperature of 160 °C - 240 °C.
• step (c) the stretching in the MD direction is carried out at 80 °C - 120 °C with a stretching ratio of 4 to 7, and the stretching in the TD direction is carried out at 90 °C - 130 °C with a stretching ratio of 4 to 12.
• the heat-setting comprises an oven heat treatment and a roller heat treatment, and preferably, the oven heat treatment has a temperature of 120 °C - 150 °C, and the roller heat treatment has a temperature of 50 °C - 70 °C.
• the polyolefin resin is selected from polyethylene (including, for example, LDPE, LLDPE, HDPE, UHDPE), polypropylene, polybutene, polymethylpentene, a copolymer thereof, or a mixture thereof.
• polyolefin as used herein may be a polyolefin monomer (i.e., a single type of polyolefin), a polyolefin copolymer, or a polyolefin mixture.
• mixture refers to a physical mixture of two or more homopolymers with different molecular structures, two or more copolymers with different molecular structures, or both homopolymer and copolymer that have different molecular structures.
• the mixture may include different polymers, i.e., at least two polymers with different chemical properties (such as polyethylene, polypropylene, and/or a copolymer of ethylene and propylene with different chemical properties); and/or polymers with the same chemical property but different characteristics (such as two different types of polyethylene with different characteristics (e.g., density, molecular weight, molecular weight distribution, rheology, additive (composition and/or percentage), etc.)).
• machine direction refers to a direction in which the machine is operated.
• transverse direction refers to a direction perpendicular to a direction in which the machine is operated.
• a first aspect of the present invention provides a microporous separator for lithium battery including a polyolefin resin.
• the microporous separator has a melt index of 0.04 g/10min - 3 g/10min, preferably 0.08 g/10min - 0.4 g/10min; the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight of 2 million to 5 million in the microporous separator is 5 mol% - 8 mol%, preferably 5 mol% - 7 mol%; a resilience speed of the microporous separator in its thickness direction is greater than or equal to 2 ⁇ 10 -4 ⁇ m/s, preferably greater than or equal to 3 ⁇ 10 -4 ⁇ m/s, greater than or equal to 5 ⁇ 10 -4 ⁇ m/s, greater than or equal to 7 ⁇ 10 -4 ⁇ m/s, greater than or equal to 8 ⁇ 10 -4 ⁇ m/s, and most preferably greater than or equal to 10 ⁇ 10 -4 ⁇ m/s
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million in the microporous separator accounts for 0 mol% - 1 mol%, preferably 0.5 mol% - 1 mol%.
• the polyolefin resin may be any polyolefin resin commonly used in the art for preparing a microporous separator for lithium battery, for example, it may be selected from polyethylene (including, for example, LDPE, LLDPE, HDPE, UHDPE), polypropylene, polybutene, polymethylpentene, a copolymer thereof, or a mixture thereof, with polyethylene and/or polypropylene being preferred.
• the polyolefin resin may be used as long as it is capable of producing the microporous separator for lithium battery required by the present invention.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million in the polyolefin resin is 0 mol% - 2 mol%, preferably 1 mol% - 1.5 mol%.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight of 2 million to 5 million in the polyolefin resin is 5 mol% - 9 mol%, preferably 5 mol% - 8 mol%, and more preferably 6 mol% - 8 mol%.
• a molecular weight distribution of the polyolefin resin is between 3 and 5, preferably between 3.5 and 4.5.
• the microporous separator satisfies one or more combinations of the following:
• the microporous separator of the present invention is preferably a separator prepared by a wet process.
• the average pore diameter of the microporous separator may be 25 nm - 50 nm, preferably 30 nm - 45 nm, and the thickness of the microporous separator may be 1 ⁇ m - 30 ⁇ m, preferably 4 ⁇ m - 12 ⁇ m.
• a second aspect of the present invention provides a preparation method for a microporous separator for lithium battery, including the following steps:
• a microporous separator having excellent resilience performance in the thickness direction can be obtained, which is suitable for applications in lithium batteries.
• the polyolefin resin may be any polyolefin resin commonly used in the art for preparing a microporous separator for lithium battery, for example, it may be selected from polyethylene (including LDPE, LLDPE, HDPE, UHDPE), polypropylene, polybutene, polymethylpentene, a copolymer thereof, or a mixture thereof, with polyethylene and/or polypropylene being preferred.
• the plasticizer is a small-molecule solvent that can dissolve the polyolefin resin, for example, it may be liquid paraffin, diethyl phthalate, palm oil, etc., preferably, liquid paraffin having a kinematic viscosity of 35 mm 2 /s - 120 mm 2 /s at 40 °C, and further preferably liquid paraffin having a kinematic viscosity of 40 mm 2 /s - 55 mm 2 /s at 40 °C.
• the testing method for kinematic viscosity is based on GB/T 265.
• a weight ratio of the polyolefin resin to the plasticizer is preferably between 15:85 and 35:65, and more preferably between 18:82 and 23:77.
• the weight ratio of the polyolefin resin to the plasticizer may be 15:85, 16:84, 17:83, 18:82, 19:81, 20:80, 21:79, 22:78, or 23:77, etc.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million is 0 mol% - 2 mol%, preferably 1 mol% - 1.5 mol%.
• the molecular weight distribution of the polyolefin resin is in a range of 3-5, preferably 3.5-4.5.
• the treatment in step (a), may be carried out using any of the existing methods capable of forming the mixture into a melt, for example, an extruder may be used for melt blending.
• parameters of the extruder include: an extruder temperature of 150 °C - 260 °C, preferably 180 °C - 250 °C, and an extruder screw speed of 60 r/min - 125 r/min, preferably 70 r/min - 90 r/min.
• step (b) the method of extruding and solidifying the melt into a thick sheet is capable of forming a thick sheet of a desired thickness.
• the inventors of the present invention also found through in-depth research that controlling the parameters of the extrusion step in the separator manufacturing process helps to control the compression resistance of the separator. Under the condition of fixed extrusion quantity, the thick sheet in step (b) can be achieved by matching the die lip opening and casting speed.
• the die lip opening is a
• the thickness of thick sheet is h
• control of the expansion coefficient A may be achieved by the roll speed of casting roller, the melt flow rate out of the die, and the die lip opening together.
• the melt flow rate out of the die may be comprehensively adjusted by the extruder screw speed and the temperature of die.
• the roll speed of the casting roller may be 3 m/min - 8 m/min, preferably 5 m/min - 6 m/min; the temperature of die may be 160 °C - 240 °C, preferably 180 °C - 220 °C. Preferably, the temperature of the casting roller may be 20 °C - 60 °C.
• the die lip opening may be 0.5 mm - 4 mm, preferably 0.8 mm - 3 mm.
• the thick sheet is stretched to obtain a stretched sheet, and the stretching includes a stretching in the MD direction and a stretching in the TD direction.
• the stretching in the MD direction may be carried out before the stretching in the TD direction; or, the stretching in the TD direction may be carried out before the stretching in the MD direction, with the former being preferred.
• the stretching in the MD direction is carried out at 80 °C - 120 °C with a stretching ratio of 4 to 7 and the stretching in the TD direction is carried out at 90 °C - 130 °C with a stretching ratio of 4 to 12.
• the stretching in the MD direction is carried out at 95 °C - 110 °C with a stretching ratio of 6 to 8
• the stretching in the TD direction is carried out at 105 °C - 125 °C with a stretching ratio of 6 to 10.
• the plasticizer in the stretched sheet may be removed by means of circulation feed of the extraction agent.
• the circulation feed rate of the extraction agent is preferably 1 m 3 /h - 5 m 3 /h.
• the stretched sheet may be heated for drying by means of one or more of a hot roller, a heating plate, or a hot air.
• a drying temperature is 20 °C - 150 °C.
• the heat-setting may include an oven heat treatment and a roller heat treatment.
• the temperature of the oven heat treatment is 120 °C - 150 °C and the temperature of the roller heat treatment is 50 °C - 70 °C.
• the time for oven heat treatment may be 2 s -30 s, and the time for roller heat treatment may be 5 s -60 s.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight of 2 million to 5 million accounts for 5 mol% - 8 mol%, preferably 5 mol% - 7 mol%.
• the quantity proportion of polyolefin chain segment ingredients with a weight-average molecular weight greater than 5 million and below 9 million accounts for 0 mol% - 1 mol%, preferably 0.5 mol% - 1 mol%.
• the resilience speed of the microporous separator in the thickness direction is greater than or equal to 2 ⁇ 10 -4 ⁇ m/s, preferably, greater than or equal to 3 ⁇ 10 -4 ⁇ m/s, greater than or equal to 5 ⁇ 10 -4 ⁇ m/s, greater than or equal to 7 ⁇ 10 -4 ⁇ m/s, greater than or equal to 8 ⁇ 10 -4 ⁇ m/s, and most preferably greater than or equal to 10 ⁇ 10 -4 ⁇ m/s.
• a third aspect of the present invention provides a microporous separator for lithium battery obtained by the preparation method of the second aspect of the present invention.
• the polyethylene resin having a melt index of 0.1 g/10min and a molecular weight distribution of 4.5 was mixed with a plasticizer (paraffin oil with a kinematic viscosity of 45 mm 2 /s at 40 °C) in a weight ratio of 28:72, and then melted and blended through an extruder to form a melt; where, in the polyethylene resin, the quantity proportion of polyethylene chain segments with a weight-average molecular weight of 2 million to 5 million was 6%, and the quantity proportion of polyethylene chain segments with a weight-average molecular weight greater than 5 million and below 9 million was 1.3%.
• the extruder temperature was 220 °C, and the extruder screw speed was 80 r/min.
• the above-mentioned melt was cooled and solidified by a casting roller to form a thick sheet, with a temperature of casting roller of 25 °C.
• the obtained thick sheet was subjected to a stretching treatment, with a stretching temperature of 95 °C and a stretching ratio of 6.3 in the MD direction; and a first stretching temperature of 110 °C and a stretching ratio of 6 in the TD direction.
• Microporous separators are prepared with reference to the method of Example 1, and the differences between the preparation methods for microporous separator specifically adopted in Examples 2 to 12 as well as in Comparative Examples 1 to 2 and the preparation method of Example 1 are detailed in Table 1, where the parameters of Examples 2 to 12 as well as in Comparative Examples 1 to 2 which are not embodied in Table 1 are the same as those in Example 1.
• Microporous separators are prepared with reference to the method of Example 2, and the differences between the preparation methods for microporous separator specifically adopted in Examples 2-1 to 2-3 and the preparation method of Example 2 are detailed in Table 2, where the parameters of Examples 2-1 to 2-3 which are not embodied in Table 2 are the same as those in Example 2.
• Example 1 Microporous separator Raw material Quantity proportion of polyolefin chain segments with a weight-average molecular weight of 2 million to 5 million /% Quantity proportion of polyolefin chain segments with a weight-average molecular weight greater than 5 million and below 9 million /% Melt index g/10min Quantity proportion of polyolefin chain segments with a weight-average molecular weight of 2 million to 5 million /% Quantity proportion of polyolefin chain segments with a weight-average molecular weight greater than 5 million and below 9 million /% Melt index g/10min Molecular weight distribution Example 1 5.3 1 0.13 6 1.3 0.1 4.5
• Example 2 6.2 1 0.11 7 1.3 0.08 4.5
• Example 3 7.4 1 0.07 8 1.2 0.05 4.5
• Example 4 7.9 1 0.04 9 1.3 0.01 4.5
• Example 5 6.2 0 1.6 7 0 1.4 4.5
• Example 6 6.2 0.5 1.5 7 0.2 1.2 4.5
• the resilience speed, resilience recovery rate, compression deformation rate, and resilience deformation rate of the microporous separator all decrease in a unified trend as the quantity proportion of polyolefin chain segments with a weight-average molecular weight of 2 million to 5 million increases.

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• Cell Separators (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
• Electric Double-Layer Capacitors Or The Like (AREA)

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